1. Field of the Invention
The present invention relates to a switched reluctance motor (hereinafter, referred to as xe2x80x9cSRMxe2x80x9d), and more particularly, a method of controlling alignment of a rotor of an SRM with respect to a stator and an SRM driving circuit for realizing the same in which current flowing into phase coils surrounding each stator salient pole pair in respective motor phases of a stator of the SRM is detected upon the starting of the SRM to compare the magnitude values of the detected current with each other so that the alignment of a rotor with respect to the stator is controlled in such a fashion that rotor salient pole pair of the rotor is brought into alignment with a corresponding stator salient pole pair of a specific motor phase with a phase coil into which current of the lowest level flows, thereby shortening the starting time of the SRM and reducing a noise generated upon the initial alignment of the rotor with respect to the stator.
2. Description of the Related Art
A synchronous motor is a type of an alternating current (AC) motor, in which a change of an excitation state of the motor allows for adjustment of its power-factor, and which rotates at a synchronous speed despite a variation of a load.
The SRM has the same characteristics as that of such a synchronous motor, but refers to a motor which does not have a direct current (DC) excitation state and operates synchronously by a reluctance torque produced by an unbalanced distribution of a magnetic reluctance due to the relative position between the stator salient pole pairs of the stator and the rotor salient pole pairs of the rotor.
FIG. 1 is a cross-sectional view illustrating an example of a typical three-phase SRM.
Referring to FIG. 1, there is shown a three-phase SRM 100 including a stator having a plurality of radially inwardly extending stator poles 101p configured as diametrically opposed stator salient magnetic pole pairs Axe2x80x94A, Bxe2x80x94B, Cxe2x80x94C around each which a phase coil (i.e., the windings around any two diametrically opposed stator salient poles connected in series or in parallel to define a motor phase) 101c is wound, and a rotor 102 disposed about a shaft within the stator 101 and having a plurality of radially outwardly extending rotor poles 102p configured as diametrically opposed rotor salient pole pairs for rotating by a reluctance torque produced by an unbalanced distribution of a magnetic reluctance due to the relative position between the stator salient pole pairs 101p of the stator 101 and the rotor salient pole pairs 102p of the rotor 102.
The driving of the SRM 100 having such a configuration requires detection of the position of the rotor 102. At least one sensor is generally used to detect the position of the rotor 102. In the case of a single sensor three-phase SRM using one sensor for detecting the position of the rotor 102, a pair of rotor salient pole 102p of the rotor 102 must be aligned previously with a pair of corresponding stator salient pole 101p, i.e., Axe2x80x94A, Bxe2x80x94B, or Cxe2x80x94C of the stator 101 in a predetermined motor phase for the initial starting of the SRM 100. However, in such a three-phase SRM 100, when the pair of rotor salient pole 102p is brought into misalignment with the pair of corresponding stator salient pole Axe2x80x94A, Bxe2x80x94B, or Cxe2x80x94C in the predetermined motor phase, it cannot be moved toward the precise alignment position with the corresponding stator salient pole pair Axe2x80x94A, Bxe2x80x94B, or Cxe2x80x94C. In order to resolve the above misalignment problem, as shown in FIG. 2, the prior art has adopted a method in which the nearest rotor salient pole pair 102p is aligned sequentially with each corresponding stator salient pole pair 101p in each motor phase in the order of phase Axe2x86x92phase Bxe2x86x92phase C in three motor phases (i.e., phase A, phase B and phase C) to bring the nearest rotor salient pole pair 102p into alignment with the corresponding stator salient pole pair 101p in a desired phase among three motor phases A, B and C while avoiding the misalignment, and a method in which the nearest rotor salient pole pair 102p is aligned sequentially with each corresponding stator salient pole pair 101p in each motor phase in the order of phase Axe2x86x92phase B in three motor phases A, B and C to bring the nearest rotor salient pole pair 102p into alignment with the corresponding stator salient pole pair 101p in a desired phase among three motor phases A, B and C while avoiding the misalignment. At this time, a voltage pulse is applied to the phase coil surrounding the corresponding stator salient pole pair 101p in the desired phase so that the nearest rotor salient pole pair 102p is brought into alignment with the corresponding stator salient pole pair 101p. That is, as shown in FIG. 2, the voltage pulse having a constant width is first applied to the phase coil surrounding the corresponding stator salient pole pair 101p at a relatively long interval. Then, after applying the voltage pulse several times, the interval of the voltage pulse is reduced gradually and the voltage pulse is applied continuously until its interval is reduced to a desired interval to bring the nearest rotor salient pole pair 102p into alignment with the corresponding stator salient pole pair 101p around which the energized phase coil is wound in a desired phase.
However, in the above conventional rotor alignment method, after the nearest rotor salient pole pair 102p is first aligned with a corresponding stator salient pole pair 101p for a desired phase among three motor phases A, B and C, the nearest rotor salient pole pair 102p is aligned with a corresponding stator salient pole pair 101p around which an energized phase coil is wound for the next phase. At this time, in alignment of each rotor salient pole pair of the rotor 102 of the SRM 100, the farther a rotor salient pole pair 102p of the rotor 102 is from a corresponding stator salient pole pair 101p for alignment, the more current become to flow into the phase coil (the windings) 101c surrounding the corresponding stator salient pole pair 101p. Moreover, such large amount of current generates a high noise when bringing each rotor salient pole pair 102p of the rotor 102 into alignment with each corresponding stator salient pole pair 101p of the stator 101. Further, as described above, the nearest rotor salient pole pair is aligned sequentially with each corresponding stator salient pole pair in each corresponding motor phase in three phases or two phases alignment manner in order to avoid the misalignment of the rotor, thereby lengthening the starting time of the motor.
Therefore, the present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a method of controlling alignment of a rotor of an SRM and an SRM driving circuit for realizing the same which shortens the starting time of the SRM and reduces a noise generated upon the initial alignment of each rotor salient pole pair of the rotor with respect to each corresponding stator salient pole pair of the stator.
According to one aspect of the present invention, there is provided a method of controlling alignment of a rotor of an SRM with respect to a stator, the SRM including a stator having a plurality of diametrically opposed stator salient magnetic pole pairs around each which each of a plurality of phase coils is wound, and a rotor disposed about a shaft within the stator and having a plurality of diametrically opposed rotor salient pole pairs, comprising the steps of:
(a) applying a voltage pulse having an identical magnitude to each phase coil surrounding the plurality of pairs of stator salient magnetic poles in a plurality of respective motor phases of a stator of the SRM upon the initial starting of the SRM;
(b) detecting current flowing into the each phase coil in the plurality of respective motor phases, respectively, in accordance to the application of the voltage pulse;
(c) comparing the respective magnitude values of the detected current in the respective motor phases with each other; and
(d) bringing rotor salient pole pair of the rotor into alignment with a corresponding pair of stator salient poles of a motor phase with a phase coil into which current of the lowest level flows with the result of the comparison.
Preferably, in the step (a), the voltage pulse may be sequentially applied to the each phase coil surrounding the plurality of diametrically opposed stator salient magnetic pole pairs in the plurality of respective motor phases of the stator of the SRM.
Preferably, the steps (a) and (b) may be repeatedly performed several times to improve reliability for the comparison of the magnitude values of the detected current in the step (c).
Also, preferably, the step (b) is performed in a predetermined point of time before the value of the voltage pulse value becomes zero (0) after the application of the voltage pulse.
Preferably, the step (c) may be performed by mutual comparison of values obtained by accumulatively adding the respective magnitude values of the current in the respective motor phases detected in the step (b).
Also, preferably, the step (d) may be performed by applying the voltage pulse having a constant width to the phase coil of the motor phase into which the current of the lowest level flows in such a fashion that the interval of the voltage pulse is reduced gradually, or by applying the voltage pulse having the constant width to the phase coil of the motor phase into which the current of the lowest level flows in such a fashion that upper and lower current limits of the current to flow into the phase coil are preset and the application of the voltage pulse is interrupted if the current reaches the upper current limit and the voltage pulse is applied again if the current reaches the lower current limit.
According to another aspect of the present invention, there is also provided a driving circuit for driving an SRM, the SRM including a stator having a plurality of diametrically opposed stator salient magnetic pole pairs around each which each of a plurality of phase coils is wound, and a rotor disposed about a shaft within the stator and having a plurality of diametrically opposed rotor salient pole pairs, comprising:
a plurality of switching means adapted to switch on/off the flow of current into each of the plurality of phase coils surrounding each of the plurality of diametrically opposed stator salient magnetic pole pairs of the stator, the plurality of the switching means each being connected in series across each of the phase coils;
a plurality of diodes adapted to control the inputting and outputting of the current into and from each of the phase coils only in the one direction, the plurality of the diodes each being connected in parallel to a current input terminal and a current output terminal of each of the phase coils; and
a resistor adapted to detect the current flowing into each of the phase coils, the resistor being connected in series to the current output terminal of each phase coil.